It was narrated that Ibn ‘Abbas (رضي الله عنه) said:

A man of Banu Sulaim passed by a group of the Companions of the Prophet (ﷺ) driving some sheep of his, and he greeted them with salam. They said: He only greeted you with salam to protect himself from you. So they went to him and killed him, then they took his sheep and brought them to the Prophet (ﷺ). Then Allah revealed the words: “O you who believe! When you go (to fight) in the Cause of Allah, verify (the truth), and say not to anyone who greets you (by embracing Islam): ‘You are not a believer'...” [an-Nisa' 4:94].